The present invention is directed to a process for the preparation of organic phosphites, specifically for improving the purity of organic phosphites.
Organic phosphites are typically prepared from reactions between phosphorous compounds, e.g., phosphorous trihalides, and an excess amount of appropriate hydroxy compounds. Examples of the hydroxy-substituted aromatic compounds used in the reaction include nonylphenol, dodecylphenol, 2-t-butylphenol, 2,4-di-t-butylphenol, 2-(1,1-dimethylpropyl) phenol, 2,4-di-t-amylphenol, 2-t-octylphenol, 2,4 di-t-octylphenol, and the like. The reaction is commonly carried out in the presence of a solvent and/or a hydrogen halide acceptor to increase the rate of reaction, e.g., amines such as t-butylamine, t-pentylamine, t-hexylamine, t-octylamine, di-t-butylamine, di-t-pentylamine, di-t-hexyamine, di-t-octylamine, tripropylamine, tributylamine, trimethylamine, triethylamine, N,N-dimethylaniline, N,N-diethylaniline, Hunig base or N,N-dimethyl-aniline and the like.
It is known that the presence of excess/unreacted hydroxy compounds and solvents such as heptane or amines in the organic phosphite product may negatively affect the product quality, e.g., color discoloration. U.S. Pat. No. 5,532,401 discloses a process to remove excess nonylphenyl from the synthesis of tris(nonylphenyl)phosphite using vacuum thin film distillation, i.e., at vacuum levels of about 1-10 mm Hg and temperatures of about 100-350xc2x0C.
There is still a need for an improved process for the production of organic phosphites and for improving the purity of organic phosphites.
The invention relates to a process for manufacturing organic phosphites comprising: reacting a hydroxyl-containing compound with a phosphorous compound in the presence of an amine acid acceptor and desorbing residual hydroxyl-containing compound in the reaction product in a desorbing column employing an inert gas as a desorbing agent.
The invention also relates to a process to purify organic phosphites containing residual hydroxyl-containing compounds by desorbing the residual hydroxyl-containing compound in the reaction product in a desorbing column employing an inert gas as a desorbing agent.
Organic phosphites are typically produced by reacting a phosphorous compound with hydroxyl-containing compounds wherein the halides are displaced by the hydroxyl-containing compounds. The organic phosphites of the present invention include phosphonites of the formulae:
(RO)2Pxe2x80x94R
or
Pxe2x80x94(OR)3
where each R is independently selected from alkyl, aryl, alkaryl, aralkyl and substituted alkyl, aryl, alkaaryl and arakyl groups. Examples of organic phosphites include triphenyl phosphite, tris(2,5-di-tert-butylphenyl)phosphite, tris(2-tert-butylphenyl)phosphite, tris(2-phenylphenyl)phosphite, tris(2-(1,1-dimethylpropyl)phenyl)phosphite, tris(2-cyclohexylphenyl)phosphite, tris(2-tert-butyl-4-phenylphenyl)phosphite, tris(2-tert-butyl-4-methylphenyl)phosphite, tris(2,4-di-tert-amylphenyl)phosphite and tris(2,4-di-tertbutylphenyl)phosphite.
1. Reaction to produce organic phosphites. In one embodiment of the invention, organic phosphites are typically produced by reacting a phosphorous halide with hydroxyl-containing compounds wherein the halides are displaced by the hydroxyl-containing compounds. In another embodiment of the invention, organic phosphites are produced from reactions between di-substituted phosphites and hydroxyl-containing compounds wherein the halogen group is displaced by the hydroxyl-containing compounds. In yet a third embodiment, organic phosphites are disphosphites based upon pentaerythritol and prepared from the reaction of pentaerythritol, phosphorous trihalide, and a hydroxyl-containing compound.
Reactant 1xe2x80x94phosphorous compounds. In embodiments wherein phosphorous halides are used, examples of the halide compounds include chlorine, fluorine, bromine, iodine and mixtures thereof. In one embodiment, the halide compound is phosphorous trichloride. In another embodiment, phosphorous tribromide is used.
In embodiments wherein di-substituted phosphites are used, the di-substituted phosphite is a di-substituted phosphorohalidite of the general formula: 
wherein each of R1 and R2 are independently a C1-20 alkyl, aryl, or alkaryl moiety and Y is a halogen. In another embodiment, R1 and R2 are interconnected (i.e., the residual of a diol) such that the di-substituted phosphite is a cyclic phosphite. An example is 2-butyl-2-ethyl-1,3-propanediol-monochlorophosphite.
Reactant 2xe2x80x94phenolic compounds. Examples of the hydroxyl-containing compounds in the present invention include but not limited to 2-t-butylphenol, 2,4-di-t-butylphenol, 2-(1,1-dimethylpropyl) phenol, 2,4-di-t-amylphenol, 2-t-octylphenol, 2,4 di-t-octylphenol, 2-t-nonylphenol, 2-t-dodecyl -phenol, 2-(dimethylbenzyl)phenol, and dodecylphenol. In one embodiment, nonylphenol is used.
Optional acid acceptors for increasing the conversion rate. The reaction to prepare organic phosphites is typically promoted, for example, by the use of additional acid acceptors or dehydrohalogenation agents well-known in the art, including amines, pyridines, pyrrolidines, amides, an aqueous alkalide material, or a hydroxide of alkaline metal or alkaline earth metal.
The amines may be primary amine, secondary amine, and tertiary amine commonly used in the art. Examples of the amines include t-butylamine, t-pentylamine, t-hexylamine, t-octylamine, di-t-butylamine, di-t-pentylamine, di-t-hexyamine, di-t-octylamine, tripropylamine, tributylamine, trimethylamine, triethylamine, N,N-dimethylaniline, N,N-diethylaniline, Hunig base or N,N-dimethyl-aniline and the like. In one embodiment, tripropylamine is used as the dehydrohalogenation agent.
Optional organic solvent. In one embodiment of the invention, an organic solvent is used. The organic solvent may be any solvent that does not inhibit the reaction, and is not specifically limited. Examples thereof include aromatic hydrocarbon, aliphatic hydrocarbon, oxygen-containing hydrocarbon, halogenated hydrocarbon and the like. Examples of solvents include heptane, benzene, toluene, xylene, methyl ethyl ketone, acetone and the like. In one embodiment, heptane is used.
2. Preparation of the organic phosphites. The reaction to prepare organic phosphites is performed in devices known to be suitable for the purpose. In general, the hydroxyl-containing compound is placed, optionally together with a solvent, into a reaction vessel. The phosphorous compound is then added, and after addition of at least an optional acid acceptor, the reaction mixture is stirred until the reaction is complete. Stirring is preferably carried out with heating of up to about 200xc2x0 C. in order to accelerate the reaction. After the reaction has reached equilibrium, any optional solvent used in the reaction may be removed by flash distillation.
3. Purification of organic phosphite end-product. As noted before that there can be an excess amount of phenolic compounds including unreacted phenols plus a small amount of solvents left in the product stream, collectively called xe2x80x9cresidual phenol.xe2x80x9d Applicants have found that the excess phenol can be removed in a simple separation step at about atmospheric pressure and relatively low temperature using standard operational apparatuses such stripping type columns, for purified organic phosphites having less than 0.5 wt. percent phenolic compounds.
In the next purification stage of the process, the residual phenol is removed in the presence of an inert/non-reactive gas and surface enhancer such as packing in a column. Examples of non-reactive gas include nitrogen, hydrogen, argon, and carbon dioxide. The column pressure is maintained at about atmospheric pressure. The column temperature is maintained in a range of about 100xc2x0 C. to about 300xc2x0 C.
In one embodiment of the invention, the column is maintained at about 150-200xc2x0 C. via the use of hot oil circulating in the jacket of the column.
In another embodiment of the invention, the incoming non-reactive gas is pre-heated to a temperature of about 150-200xc2x0 C. before scrubbing.
In one embodiment of the invention, the feed organic phosphite stream to be scrubbed is applied to the top of the column, while a controlled nitrogen gas feed flows in counter-current thereto through the packing bed of the desorber from bottom to top of the column. The descending liquid stream being rich in residual phenols countercurrently contacts the ascending heated nitrogen stream and the dissolved residual phenols are extracted from the organic phosphite stream by the heated nitrogen as vapors. The inert gas and desorbed phenol stream exits the top of the column and passes by a condenser where it is cooled down to about 50xc2x0 C. The purified organic phosphites are withdrawn at the bottom of the desorber.
In yet another embodiment of the invention, the purified organic phosphite stream withdrawn from the desorber is used as a feed stream to yet another desorber connected in series for further removal of any residual phenols from the organic phosphites to obtain maximum purity in the end-product of less than 0.1 wt. % impurities.